Bioethanol as an example of bioalcohols is produced mainly by decomposing and purifying sugar in corn, wheat, etc. Bioethanol has been widely used throughout the world in recent years, as an alternative fuel to petroleum (gasoline) or as a fuel mixed with gasoline. The usage of bioethanol is thus increasing every year.
However, despite an increase in handling of bioethanol in processes such as storing and transporting bioethanol or mixing bioethanol with gasoline, the high local corrosiveness of bioethanol, in particular its property of causing pitting corrosion and stress corrosion cracking (SCC), makes the handling of bioethanol difficult.
The high corrosiveness of bioethanol is due in part to the presence of acetic acid or chloride ions as infinitesimal impurities in the bioethanol production process or the absorption of water or dissolved oxygen during storage.
There is thus a drawback in that bioethanol can be safely handled only in facilities with ethanol resistance measures, e.g. facilities using organic coating materials, stainless steel, or stainless clad steel having excellent ethanol-induced SCC resistance, as bioethanol storage facilities. Besides, conventional pipelines for transporting petroleum, etc., cannot be used for transportation of bioethanol.
Hence, a problem lies in that facilities for handling bioethanol require considerable cost.
To solve the aforementioned problem, Patent Literature (PTL) 1 as an example proposes a method of applying a zinc-nickel coating containing 5% to 25% Ni to a steel material for tanks for biofuels, and performing a chemical conversion treatment containing no hexavalent chromium on the coating. This method is described to achieve favorable corrosion resistance in ethanol-containing gasoline.
PTL 2 proposes a steel sheet for pipes having excellent corrosion resistance by applying a “Zn—Co—Mo coating where the composition ratio of Co to Zn in the coating layer is 0.2 at % to 4.0 at %” to the steel sheet surface, for fuel vapor of bioethanol and the like.
Non-patent Literature (NPL) 1 investigates the inhibitor effect of ammonium hydroxide against stress corrosion cracking (SCC) of a steel material in a bioethanol simulated liquid. NPL 1 reports that the addition of ammonium hydroxide suppresses crack growth and mitigates SCC.